It is often necessary to control the radius of curvature of a mirror to control precisely the location of the focal point, for example, in the case of the use of lasers in machining operations or to compensate for changes in other optical components due to heating of the mirror or other physical changes.
Among the methods commonly used to achieve such control of the radius of curvature of a mirror is that which utilizes pressure on the rear surface of the mirror while the outer periphery thereof is held in a constant position, thus resulting in the desired corrective distortion of the mirror. Such methods include those disclosed in: U.S. Pat. No. 6,253,619 to Danyluk et al, issued Jul. 3, 2001 that describes an adjustable acoustic mirror in which the curvature is adjusted with a screw, rod or voltage modulator; U.S. Pat. No. 6,260,976 to Endou et al, issued Jul. 17, 2001 that describes a laser beam collimation device in which the collimation mirror is convex in its initial state but may be changed in its radius of curvature by a piezolectric actuator pressing from the rear side; and U.S. Pat. No. 4,295,710 to Heinz, issued Oct. 20, 1981 that describes a multi-actuator deformable mirror for correcting wavefront aberrations in a laser fusion optical system which comprises a copper-surfaced aluminum faceplate supported by a plurality of ball screw mirror actuator assemblies. In the last assembly, a copper coating is provided on the rear of the faceplate to mitigate bimetal distortion effects.
While each of these and similar prior art radius of curvature control devices provide adequate control in many applications, they are relatively complex, and often do not provide a perfectly spherical distortion of the mirror.
There is therefore, a need for a relatively simple radius of curvature control system that provides nearly spherical distortion of the mirror in response to external influences, especially heating.